our report from our chief education correspondent, rehema ellis. >> reporter: the college classroom is changing. courses from some of the world's most elite universities are now available to anyone for free. at a furious pace, schools are participating with start-up companies like coursera to deliver online courses. or m.o.o.k.s. >> much faster than any of us were expecting. we reached our first 1 million users faster than facebook. >> reporter: physics, poetry, astronomy, even guitar, all just a click away. university of virginia retooled his modern history course for this semester's online debut. the class usually open to 120 students saw enrollment soar. >> 42,000 students around the world. >> reporter: to put it in perspective, in order to reach the same number of students, this professor would have to teach his course here at the university of virginia for 350 years. since 2011, some 2.5 million students from hundreds of countries have signed on, even though m.o.o.k.s are not offered for credit and completion rates are low, some educators say the potential exists to revolutionize